The fabrication of tungsten contacts requires the use of a metal liner with two components: a barrier layer and oxygen getter film. The barrier layer is commonly TiN and serves to avoid fluorine diffusion of a WF6 precursor towards the oxygen getter ion metalized plasma (IMP) titanium, that is commonly used in the contact formation process.
However, the reaction of fluorine with Ti causes distortion of the profile at the top of the contacts for early pinch-off during W metal fill. This causes a hollow contact defect. This fluorine-titanium reaction can also disrupt the bottom of the contact to form titanium fluoride substances that can increase contact resistance (Rc). In an attempt to mitigate some of these issues, processes have used thicker TiN layer films. Although this may mitigate some of the issues, increasing the thickness can also bring a penalty in contact resistance by increasing the barrier to electron conduction.